This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 198 60 272.3, filed on Dec. 24, 1998 the entire disclosure of which is incorporated herein by reference.
The invention relates to a method and a circuit arrangement for reducing the level of noise produced during actuation of an electromagnetically actuated device, whereby such noise results from excessive acceleration and deceleration of an armature of the device when an excessive actuating current has been applied to the device.
Various types of electromagnetically actuated or operated devices, such as electromagnetic valves and relays for example, are known in the art. Such devices typically comprise an electromagnet including a magnetic coil as well as a movable armature, which is moved or changed in position when a sufficient actuating current is applied to the magnetic coil. More particularly, the armature begins to move once the actuating current has reached a predetermined minimum threshold value as the current is increased from a minimum or zero value up to its maximum operating value. Typically, however, the maximum or full actuating current applied to the magnetic coil during the actuation exceeds the minimum threshold level that is necessary for moving and thereby actuating the armature. As a result, the armature is very strongly and excessively accelerated and driven against a mechanical end limit stop or the like.
The rapid excessive acceleration of the armature, and especially the impact of the excessively accelerated armature against its mechanical end limit stop results in the transfer and conversion of excessive amounts of energy. Most importantly, the kinetic energy of the moving armature is converted largely into sound energy and deformation or wear energy when the armature abruptly stops by impacting against the mechanical end limit stop. The greater the actuating current that is applied to the magnetic coil, the greater will be the acceleration and the ultimate velocity and energy of the armature, and thus also the greater will be the amount of noise and wear produced when the armature impacts against the end limit stop. It is therefore desirable to actuate the electromagnet with the lowest possible actuation current that will still effectively move the armature from its initial position to its actuated position.
Throughout this specification, the term xe2x80x9carmaturexe2x80x9d will be used to refer to any component that is driven and moved by the electromagnet or especially the magnetic coil in an electromagnetically actuated device. The process in which the armature is moved, will generally be referred to as the switching process or the actuating process of the electromagnet.
German Patent Publication DE-C2 3,425,574 discloses a method of operating an electromagnetically actuated device in the manner that has generally been described above. Particularly, the disclosed method involves increasing the actuating current provided to the magnetic coil in a gradual or progressive manner, over the entire range between the minimum current (zero amps) and the maximum current that is ultimately applied to the magnetic coil. By gradually or progressively increasing or ramping-up the actuating current, it may be expected that an excessive actuating current could be avoided, because the armature will be actuated as soon as the gradually increasing current reaches the minimum threshold value necessary for driving the armature. The point at which the plunger or armature of the electromagnet begins to move always lies within the range of this gradual or progressive increase of the actuating current, because this range extends continuously from zero amps up to the maximum amperage that is ultimately applied to the magnetic coil.
A disadvantage of such a known approach is that the specific time point of actuation of the armature is not specifically controlled or defined. Thus, if the time period within which the electro-magnetic is to be switched is relatively short, then it becomes absolutely necessary to increase or ramp-up the actuation current from zero amps up to maximum amperage with a relatively steep current increase slope so as to achieve the total ramp-up of the current in the required short time period. Unfortunately, that leads to an actuation of the electromagnet at a higher current level than would be absolutely necessary, i.e. at a higher current than the abovementioned minimum threshold level, because the current keeps rapidly increasing even as the armature is being actuated. As a result, the armature is excessively accelerated, and caused to strongly impact against the mechanical stop, which leads to a higher generation of noise and also increased wear of the various mechanical components.
In view of the above, it is an object of the invention to provide a method and a circuit arrangement that makes it possible to achieve an exact switching of the electromagnet and/or the armature of an electromagnetically actuatable device, while applying the minimum possible current to the electromagnet for achieving the actuation. More particularly, it is an object of the invention to control the operation of an electromagnetically actuatable device so that the actuation current applied to the electromagnet undergoes the smallest possible rate of increase during the time in which the actuation or switching process is carried out, while achieving the quickest possible total ramp-up of the current from zero amps to maximum amperage. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as are apparent from the present specification.
The above objects have been achieved according to the invention in a method and a circuit arrangement for controlling the actuation current applied to the electromagnet of the electromagnetically actuatable device. According to the invention, the ramp-up of the actuation current is divided into at least two or preferably three portions or ranges. An actuating range or transition function represents only a central portion of the total current variation between zero amps and maximum amps for the process of switching the electromagnet. The ramp-up current variation further includes two non-actuating ranges respectively before and after the actuating range in time. Each of the non-actuating ranges involves a steeper or more rapid increase rate of the current in comparison to the current variation that exists during the actuating range or transition function.
In the first non-actuating range, the current rapidly or steeply increases from a minimum value (e.g. zero amps) up to an initial value at the start of the actuating range. In the second nonactuating range that follows the actuating range, the current rapidly or steeply increases from the final current value of the actuating range up to the maximum value of the current that is ultimately applied to the electromagnet. If only two (rather than three) distinct ranges are used, the non-actuating range may occur before the actuating range (in which case the final current value of the actuating range is equal to the maximum amperage), or after the actuating range (in which case the initial current value of the actuating range is equal to the minimum or zero current value).
The actuating range is particularly selected to cover the time span and/or the current value range in which the switching or actuation of the electromagnet takes place. In this manner, the switching or actuation of the electromagnet is carried out with a gradually increasing current or with some other gentle variation of the current value as will be described in detail herein, while also achieving a rapid or steep increase of the current between the minimum value and the maximum value during the non-actuating ranges before and after the actuating range. Particularly, the current increase during each of the non-actuating ranges may be a substantially instantaneous current jump, limited only by the inherent inductance and available driving voltage of the circuit. Thus, the time duration of each one of the non-actuating ranges may be very brief.
One advantage of the invention is that the electromagnet can be switched or actuated using the lowest possible energy, because it is actuated at the lowest possible current value. Thereby, the invention minimizes the excess energy that is applied to the armature of the electromagnet in the form of excess acceleration, so that the generation of noise and wear on the various components such as relay contacts and the like, can be reduced or especially minimized as a consequence.
A second advantage of the invention is that the total increase of the current from a minimum value (normally zero amps) up to the ultimate maximum value can be carried out quite rapidly, without subjecting the actuation of the electromagnet to such a rapid increase of the current. This is achieved by providing a time period or range of rapid current increase both before and after the actuating range during which the electromagnet is actuated as mentioned above. In this manner, there is substantially a respective current jump from the minimum value very rapidly up to the nominal value at the beginning of the actuating range, followed by another substantial current jump from the current value at the end of the actuating range up to the maximum operating current value. It is understood that the maximum rate of the current jump characteristic is limited by inductivity of the circuit, the driving voltage, and the like. In any event, the current rise rate during the current jumps that take place in the non-actuating ranges are significantly more rapid or steep than the current variation that exists during the actuating range. For example the current increasing rate during the non-actuating ranges may be at least 8 or 10 or 15 times or even significantly more, in comparison to the current increasing rate during the actuating range.
The controlled variation of the current increasing rate or rampup characteristic as described herein can be achieved by using a semiconductor switching element in an appropriate control circuit for controlling the current flow as required. Generally, this is achieved in that the semiconductor switching element applies a controlled variable resistance in the current flow path, which thereby accordingly controls the magnitude of the current flowing through the switching element and the electromagnet. A further advantage of the three-range division of the current increasing or ramp-up characteristic is that the semiconductor switching element only has to operate for a relatively short time in an operating range in which it must provide a controlled electrical resistance. During operation in this range of controlled resistance, the semiconductor switching element generates considerable heat in accordance with the product of current and voltage (Ixc3x97V). In order to avoid overheating, this heat must be dissipated or rejected, and the operating time must be limited. According to the invention, this operating time in which the semiconductor switching element applies a controlled resistance and therefore generates substantial heat is the actuating range in which the current only gradually or progressively increases or decreases over time. On the other hand, during the initial and final non-actuating ranges, the semiconductor switching element does not apply a significant resistance, so that the current can increase in a substantial jump manner in a very short time interval (limited by the available voltage and the inductivity of the circuit), so that only a small amount of heat is generated in the semiconductor switching element during operation in these ranges.
At the end of the above described current increasing process, the current reaches its ultimate maximum value in that the semiconductor switching element is caused to operate in its lowest resistance state (non-linear saturation state), in which hardly any resistive heating arises. Thus, it is possible to operate the semiconductor switching element and therewith the electromagnet in this maximum current condition for a long period of time, for example possibly several hours, without any problems or concerns, and particularly without subjecting the semiconductor switching element to the danger of overheating or other thermal damage.
A further advantage according to the inventive manner of actuating the electromagnet is that the positive actuation of the armature of the electromagnet is absolutely ensured in each case, as long as sufficient voltage is available for driving the required current magnitude.
In an example embodiment of the invention, the time point at which the electromagnet switches is determined by any one of various technical measurement means, and a control circuit is provided for ensuring that the switching process of the electromagnet takes place within the actuating range, i.e. the range in which the current is only gradually increased, and especially within a middle portion of this actuating range. In this context, the xe2x80x9cmiddle portionxe2x80x9d refers to a portion including the center of the actuating range with respect to time or current value, and also means that the actual movement of the armature of the electromagnet only begins somewhat after the beginning of the actuating range and ends somewhat before the end of the actuating range.
The circuit arrangement is particularly embodied to achieve the advantage of correcting or compensating for any variations of the characteristics of the electromagnet or of the operating environmental conditions. For example the circuit arrangement compensates for temperature variations, which could otherwise lead to variations of the actuation of the electromagnet (for example due to the temperature dependence of mechanical friction and the like), whereby the switching process could be shifted to take place outside of the actuating range in which the current is only gently or gradually increased. Particularly, the circuit arrangement compensates for such variations of the operating characteristics by adjusting the current increasing rates and end values of the respective ranges, so that these operating characteristics do not have an effect on the actual time point or time range in which the switching process of the electromagnetic actually takes place. In this context it is further advantageous that the time point at which the switching process is initiated, and/or the time range in which the entire switching process is carried out and completed, can be rather precisely defined and tightly limited to a narrow nominal range of time and/or of current value.
One feature of the invention provides for an initial calibration sequence in order to determine at which point of the current-time curve the electromagnet switches. For this purpose, the initial calibration sequence involves once running through the entire current range from zero amps up to the maximum amperage in the form of a gradual or gently increasing curve, e.g. a linear increase. During the calibration sequence, the actuation or switching of the electromagnet is detected, and thereby the current value and/or time point at which the switching is initiated is determined by various means of measurement or detection as will be described below. Next, a limited range of time and current values around the point at which the switching of the electromagnet takes place is specified as the actuating range in which a gradual or gentle current variation is carried out according to the invention. Before this actuating range, the current will be increased rapidly from zero up to the current value of the actuating range in a jump-like manner, and after this actuating range the current will again be rapidly increased in a jump-like manner up to the maximum current value. The actuating range between the two rapid jump-like current increase ranges comprises a transition function of the current-time curve with a gentler or more gradual current rise inclination in comparison to the current rise that would be required to transition from zero amps up to the maximum amperage using a continuous gradual increasing curve as described above.
This embodiment of the invention relating to the initial calibration sequence for establishing the proper time and current values of the actuating range is especially suitable for carrying out the automatic calibrating and monitoring of devices that include a circuit arrangement according to the invention. Such calibrating can be carried out directly after manufacturing of the respective device, or after a respective specified lengthy period of operation, in order to automatically adjust, readjust, or adapt the circuit operation to the optimal switching time for the electromagnet. The values of current and/or time that are determined during such a run-through of the entire current range from zero amps up to maximum amperage can be stored in a permanent memory provided in the electromagnetically actuatable device. In this manner, the stored values will be available even after a long period of time in which the electromagnet was not in operation.
An apparatus or circuit arrangement according to the invention for carrying out the inventive method includes a control arrangement that has controllable operating parameters in order to influence the current flow characteristic of the current that is provided to the electromagnet of the electromagnetically actuatable device. The circuit arrangement advantageously further includes a memory in which the operating parameters for the control arrangement can be stored.
According to the invention, there are numerous possibilities for determining and establishing the time point or the current value at which the electromagnet switches. According to one embodiment of the invention, this is achieved by monitoring the current or the voltage that exists on the coil of the electromagnet. At the instant at which the armature (i.e. generally the movable part of the electromagnet) starts to move, the inductivity of the magnet arrangement of the electromagnet changes, and this phenomenon is detectable in a sudden voltage and current change, of which the specific time point can be determined by various technical measuring means. Additionally, according to another embodiment of the invention, the amplitude of this current variation or voltage variation can be detected. The magnitude or the energy content of this change of the current and/or voltage is an indication of the magnitude of the excess energy that is applied to the armature, which in turn is an indication of the final velocity of the armature.
In another example embodiment of the invention, the switching process is recognized or detected by a pressure sensor. If the electromagnet is a part of a valve for a fluid, then it is possible to provide and arrange a pressure sensor in such a manner so that it recognizes a variation of the pressure of the fluid that has been caused by the movement of the movable valve component connected to the armature of the electromagnet. In addition to, or instead of the above mentioned pressure sensor, other sensors may also be used. For example, a microphone may be mounted so that it detects the noise produced by the magnet and/or the valve during the switching process, and particularly when the armature or a valve head or valve disk of the valve impacts against a stop member or the like at the end of its travel range. Another alternative is the provision of an acceleration sensor that detects a shock or vibration caused by the impact contact of the movable component against an end limit stop. A further alternative is to provide a microphone that detects the shock wave in the fluid of which the flow is being controlled by the actuated valve. Thus, if a suitable selection and arrangement of the components is provided, the pressure sensor may also carry out the function of the microphone as mentioned above.
Other available possibilities and arrangements for determining the switching time point of the armature comprise a light beam switch that senses the movement of the armature, a fluid flow meter that determines the variation in fluid flow of the fluid being controlled by the valve, an electrical meter that detects the change in the load circuit being controlled by the electromagnet, for example in the case of a relay.